Ear plugs and noise filtering

You all must be experts on noise reduction, but I imagine that you are
dealing with very loud noises.

I sometimes have to work in noisy environments such as open offices
and airplanes. Most of the noise is conversation, background music,
and the like. I'm not concerned about damage to my ears -- just to my
concentration. Are there any ear plugs (or other devices) that are
effective at filtering out this kind of background noise so I can
think and concentrate?

I think I would prefer ear plugs rather than headphones because they
would be lighter and cooler, but I am open to any suggestions.

Thanks

While I am here, let me ask a seemingly opposite question. One of the
reasons I hate cocktail parties is that once the background noise gets
to a certain level (and not that high), I have a very difficult time
hearing what is being said right next to me. I can't follow a
conversation at all. This sometimes even happens in restaurants if
they are fairly noisy.

Is there anything that will filter out everything but nearby
conversation? Kinda the iopposite of the above.

Thanks, again.

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